1. Field of the Invention
The present invention generally relates to applying an adhesive to a panel, and more particularly, relates to applying a film adhesive to an acoustic face sheet for use in the aerospace industry.
2. Description of Related Art
Methods for applying an adhesive to a core of an acoustic face sheet for use in aerospace or other industries, that require sound dampening, have been known for many years. These prior art core reticulation systems, as they are known, have the film adhesive directly reticulated onto the core of the acoustic panels. After reticulation the core is connected to a surface of the acoustic panel and aligned such that the holes or perforations of the acoustic panel align with the holes of the core. The core reticulation system generally has the film adhesive softened and maintained at the softened state on the core by radiant heaters. After the film adhesive is softened on the core it is passed over an air knife in order to remove the film adhesive from the holes of the core material.
Generally, the core has a honeycomb type shape and it is desired to have the adhesive only on the top portions of the core itself and not within the orifices of the honeycomb core. In the prior art system of reticulation the core, after having the film adhesive softened, will pass through a reticulator on a wire rack that slides on rails within the reticulator. Then an air knife will direct compressed air from underneath the core and at a distance of approximately one foot away from the core. This will allow for the adhesive to be blown from around the top of each cell of the honeycomb cell structure thus in theory leaving the cell passages clear and adhesive free. The end product of the prior art core reticulation system is a core that would include film adhesive around the edge of the core cells. However, many of the prior art systems, due to the size difference of the core cells and ply holes, would have the ply holes blocked during bonding which also would lead to adhesive run off which clogs even more of the perforations in the acoustic panels. The acoustic panels generally work by absorbing sound within the perforations or orifices of the acoustic face sheet. If any of these holes are blocked or the adhesive runs off, which can cause blockage in even more holes, then the acoustic absorption ability of the acoustic face sheet is sharply reduced.
The prior art method of core reticulation encounters numerous problems during the reticulation of the core. First, the air knife used to cut or remove the skin adhesive from the core is driven by compressed air that generally includes contaminants that mix with and degrade the adhesive that is left on the ends of the core cells of the core reticulation system. These contaminants will reduce the adhesive force between the core and outer panels or skins of an acoustic face sheet. Any separation of the outer panel of the acoustic member from the core will degrade the noise absorption characteristics of the panel, reduce structural integrity and also create extraneous noise due to any vibration between the loosely connected core and outer panels. Another problem associated with the prior art core reticulation method is that the air surrounding the film adhesive is capable of cooling which leads to tears in the film adhesive on the edge of the core cells. These tears will reduce the effectiveness of the film adhesive, when the film adhesive is aligned with and secured to the panel. Furthermore, if the air cools enough and the air knife is not run at an appropriate pressure the film adhesive will not be removed from over the opening of the cell in the honeycomb core structure thus blocking the acoustic absorption for that cell and reducing the overall effectiveness of the acoustic absorption of the acoustic sheet. The prior art core reticulation method also has problems developing and having uniform fillets along the edge of the honeycomb cells. Furthermore, if the wrong angle is used for the air knife, with relation to the core, a venturi can develop within each individual cell and the fillet would not be properly formed on top of the cell thus causing a reduction in the acoustic absorption capability of any such damaged cell.
The prior art core reticulation method also generally leaves defects within the core reticulation system of greater then twenty percent. Manufacturers want the acoustic sheet panels to be less then ten percent degraded due to unopened or blocked core cells in the honeycomb core of an acoustic sheet. The noise attenuation of the acoustic face sheets is paramount in the design of modem day aerospace vehicles. The more blocked cells in the honeycomb core the less the noise absorption potential for the acoustic panel. These acoustic panels line cockpits, bodies, wings and even containment walls inside an engine, thus reduction of noise is key to the effectiveness of such products.
Therefore, there is a need in the art for a new reticulation method that will directly adhere the film adhesive to the panel instead of the edge of the honeycomb core. There is also a need in the art for a reticulation method that will reduce the amount of contamination and partially block or blocked cells in the acoustic face sheet core cells. Furthermore, there is a need in the art for a low cost method for manufacturing and building acoustic face sheet panels.